Molecular chemistry implementing reversible chemical bonds between atoms in molecules, as well as supramolecular chemistry, whose molecular components are held together by intermolecular interactions, are able to undergo a continuous change in constitution by reorganization and exchange of their building blocks. They thus define a Constitutional Dynamic Chemistry (CDC) on both the molecular and supramolecular levels. CDC takes advantage of dynamic constitutional diversity to allow for variation and selection in response to either internal or external factors to achieve adaptation. The combination of dynamics and reversibility with constitutional and structural diversity points towards the emergence of adaptive and evolutive chemistry towards systems of increasing complexity.